Typically, scientists use animals to study a new theory before they try it out in humans. But sometimes they go in the opposite direction, using animals to see whether certain theories apply only to humans. A new paper in Science does exactly that, investigating whether a widely documented human phenomenon  the fact that we tend to prefer people who behave the same way we do in social interactions  exists in other species.

It turns out it does. Adhering to the old saying "monkey see, monkey do," monkeys in the study appeared to favor those who mimicked them  even when the imitator was a member of another species (Homo sapiens). The authors of the paper, Annika Paukner of the National Institutes of Health (NIH) Animal Center and her colleague Pier Ferrari as well as two Italian researchers, structured the study this way: two experimenters, each holding a small plastic ball, faced each monkey in its cage (10 monkeys in all participated). The monkey was given an identical ball. One of the experimenters imitated whatever the monkey did with the ball  poking it, mouthing it, pounding it. The other experimenter didn't imitate the animal. (See pictures of monkeys and other animals in space.)

The advantage of mimicry was clear. Monkeys looked longer at the imitator than they did at the other experimenter, and they chose to stand in front of the imitator more often. The monkeys also exchanged little tokens (in return for a bit of marshmallow) more often with the imitator than with the nonimitator.

The study reconfirms the notion that imitation is not uniquely human (past research has also shown that apes and monkeys easily recognize when they are being copied), and that our affinity for it may have roots in our evolution. What has never been precisely understood, though, is why we like to be parroted so much. One theory is that mimicry somehow promotes safety in groups of animals by binding them together  that mimicry is a kind of social glue. (Read what fat-bellied monkeys tell us about our own social stress.)

That hypothesis certainly supports the human tendency toward reflexive imitation, a term coined in the 18th century by Adam Smith to describe the psychological act of putting yourself in someone else's shoes and experiencing their feelings  you wouldn't do that unless you were after some sort of social bond. Some years later, in 1999, the Journal of Personality and Social Psychology published an influential paper showing how socially bonding the act of mimicking can be, even when people aren't aware they're being imitated. In the study, psychologists Tanya Chartrand, who is now at Duke, and John Bargh, who is now at Yale, asked college students to describe a set of photographs in one-on-one discussions with researchers. During the discussions, the researchers subtly but consistently mirrored the mannerisms and posture of the students. If one of the college kids leaned back, then the researcher leaned back. If one of the kids folded his arms, then the researcher did as well. With a control group, the researchers made no attempt to copy behaviors; instead, they adopted a neutral tone and body language.

None of the kids noticed that the researchers were mimicking them. And yet compared with those who were not imitated, the students who were mimicked reported liking the researchers more and thinking the interaction went more smoothly. In short, when people imitate us  nodding when we do, tilting their heads when we do  we are more willing to be their ally.

Five years after Chartrand and Bargh's paper was published, a team of Dutch researchers expanded on the findings in an article in Psychological Science. The Dutch team not only replicated the earlier research but also found that people become more altruistic after they have been imitated. Mimicked participants in the Dutch study, which was conducted in the same way as the Chartrand and Bargh study, were willing to help a researcher who had "accidentally" dropped some pens 84% of the time; those in the control group helped pick up the pens only 48% of the time. The Dutch team has also found that waiters get larger tips when they use the precise words that a customer used to order food. When waiters paraphrase the order, their tips shrink  even if the order comes out of the kitchen correctly. Finally, the Dutch team discovered that people who are mimicked are more likely to donate money to charity than those who aren't.

Mimicry "may have adaptive value," the Dutch team concluded, "enhancing the chances of successful procreation of those members of a species who adopt this specific behavior."

Indeed our fondness for imitation may be a survival advantage, deeply rooted in our evolutionary biology  even monkeys become more willing to engage in a kind of commerce with those who imitate them. The practical implications are pretty obvious: if you want something from someone, a good way to get it is to imitate them. But, as the Chartrand and Bargh study suggests, do it subtly. If you're discovered copying someone's every move, you might seem a little creepy  although you could probably still fool a monkey.